There are broadly used two methods, including die pressing and cold isostatic pressing (CIP), upon pressing of powder materials into a given shape.
In die pressing, upper and lower punches and a die are provided, a space between the lower punch and the die is filled with powder, and the filled powder is compressed via reduction in a distance between the upper punch and the lower punch. In this case, friction between the powder and the die causes a pressed article having different upper, middle and lower densities.
In Cold Isostatic Pressing (CIP), when liquid pressure is applied to powder materials sealed in an easily deformable mold, such as a rubber bag, a resultant pressed article uniformly receives press force equal to the liquid pressure throughout a surface thereof and is compressed without directivity.
The aforementioned two pressings are generally performed by different apparatuses. When it is desired to equip both the apparatuses, this will cause increase in cost and an installation area. In particular, production of recent enlarged semiconductor structural ceramics often requires die pressing to be performed first and thereafter requires CIP, and investment of enormous cost is necessary to prepare both apparatuses for production of enlarged structural ceramics.
One prior art example of simultaneous implementation of cold isostatic pressing and die pressing as described above is disclosed in Korean Patent Laid Open Publication No. 10-2011-0120129 entitled “Apparatus for Powder Pressing and Cold Isostatic Pressing”.
The disclosed apparatus for powder pressing and cold isostatic pressing includes: a press unit configured to perform powder pressing; a cold isostatic press unit configured to perform cold isostatic pressing; a base frame on which the press unit and the cold isostatic press unit are mounted; a main frame installed on the base frame so as to be movable between the press unit and the cold isostatic press unit, the main frame serving as a frame for the press unit when aligned with the press unit and serving as a frame for the cold isostatic press unit when aligned with the cold isostatic press unit; and a common single pressurizer configured to apply pressure to the press unit when the main frame is aligned with the press unit and to apply pressure to the cold isostatic press unit when the main frame is aligned with the cold isostatic press unit.
The apparatus for powder pressing and cold isostatic pressing of the prior art, having the above-described configuration, may easily perform general pressing and cold isostatic pressing using both the press unit and the cold isostatic press unit.
However, the apparatus for powder pressing and cold isostatic pressing of the prior art has the following problems.
Firstly, movement of the main frame is required to arouse each process. This causes difficulty in maintaining precision in comparison with adoption of a stationary main frame. Moreover, transportation of such a heavy structure may cause time loss.
Secondly, provision of both the cold isostatic press unit to perform CIP and a hydraulic cylinder to perform die pressing results in increased manufacturing costs and requires different pressure media to apply pressure to both thereof, in turn, a greater number of hydraulic components.
Thirdly, a CIP level for loading and unloading of materials at the top of a pressure vessel differs from a die pressing level for loading and unloading of raw materials and products at a die mounting location, thus causing double staged pressing levels. This is inappropriate in terms of a movement distance of workers and makes it difficult to use transport devices for transportation of dies and products. In addition, since hydraulic components and the like are embedded in a pit below the ground level for implementation of pressing based on the nature of equipment, the invention of the prior art consequently adopts a triple stage structure including a pit level, a die pressing level above the pit level and a CIP level above the die pressing level.
In conclusion, the aforementioned apparatus of the prior art has a complicated structure, thus suffering from difficulty in repair upon occurrence of a breakdown, excessive manufacturing costs and poor management environments.